The present invention relates generally to the in situ repair of underground pipe systems, and more particularly to a method of repairing holes, cracks, and defective joints in underground drainage pipe systems such as municipal and industrial sewer systems.
Underground sanitary sewer pipe systems are designed to convey raw sewage and waste water by gravity flow to waste water treatment facilities where the sewage is processed and the waste water is treated for return to the environment. Ideally a sewer system will convey sewage and waste water to a treatment facility without leakage or spillage, but many urban sanitary sewage systems are in a state of significant disrepair. As a result of defects in sewer pipe networks, ground water surrounding sewer pipes can infiltrate into the sewer drainage systems, adding to the quantity of water which must be treated, thereby reducing the effectiveness or surpassing the capacity of waste water treatment facilities. Sewer pipes may be surrounded by ground water permanently, or on a seasonal, tidal, or rainfall related basis, any of which contributes to overload of waste water treatment facilities.
Additionally, depending on the height of the water table surrounding a sewer system, raw sewage may leak out of the sewer pipes into the surrounding soil.
Where leaking sewer pipes allow infiltration of ground water into the sewer pipes, soil particles are typically suspended in the ground water and flow into the sewer pipe, leaving voids in the soil where such suspended soil particles originated. When voids are left on the outside of the pipe, the sewer pipe no longer is supported by surrounding soil and may sag or move, increasing the size of cracks in a pipe wall or gaps between adjacent pieces of pipe. Enlarged openings through the wall of a pipe naturally permit additional infiltration of surrounding ground water, enlarging voids, until pipes eventually can collapse completely as a result of loss of support from surrounding soil.
Sewer pipes thus eventually may include longitudinal cracks, larger holes where portions of a pipe wall have collapsed, defective joints between adjacent lengths of pipe, where lengths of pipe have shifted apart or where sealing material has been carried away from a joint, and gaps or defective seals where an interconnection of a smaller pipe with a larger pipe has been disturbed.
Uncovering sewer pipes or the like to repair defects and replace defective piping is expensive, inconvenient, and dangerous, particularly where sewers are situated beneath busy streets. Nevertheless, repair must be effected or large enough voids may be created to allow the formation of potholes or sinkholes, or total collapse of streets located above such sewer pipes.
Previous attempts to deal with this problem have been disclosed, for example, in Humphreys, et al., U.S. Pat. No. 5,194,193, Nakashin U.S. Pat. No. 4,244,895, and VanDenBerg U.S. Pat. No. 1,736,293, all of which recognize and attempt to deal with the need to force sealing material through defects in a sewer pipe into an adjacent void in order to provide satisfactory repair of the sewer pipes. The sealant materials suggested by VanDenBerg and Nakashin for repairing such sewer pipes result in the need to dispose of significant quantities of sealant material which must not be left inside a sewer pipe but is not actually used to seal holes in a sewer pipe wall and is not reusable.
The method taught by Humphreys, et al., deals with excess sealant, but faces numerous problems in practice, since it teaches use of wax as a sealant, but in the presence of water, such as ground water surrounding a leaking pipe or infiltrating into a pipe through a crack or hole or similar defect, wax does not provide a tight seal. Instead, it shrinks and tends to create a porous accretion in soil by covering individual soil particles, rather than forming a solid plug or barrier and adhering to an outer surface of a pipe when the molten wax cools and becomes solid.
According to one other previously-known method for sealing underground pipes, a quantity of a catalyzed polyurethane-based grout is placed into a sewer conduit between a movable plug and a bag which is everted (or inverted, as it is often referred to in the industry) within the conduit. The grout is subjected to pressure between the bag being everted and the plug. The grout is thus forced outward through defects in the wall of the conduit and into the surrounding soil to form a seal. As the bag is everted further to cover each defect in the conduit it keeps the grout from returning through the defect into the interior. Thixotropic agents are included in the grout mix to prevent uncured material from flowing away from where it is needed to the surrounding soil or downward along the outer surface of the conduit. This method of sealing a pipe, however, does not address containment of the grout at intersections between different branches of a conduit or where the movable plug is located in a defective portion of the conduit, nor does it provide for keeping water out of the conduit or provide for recovery or disposal of grout which does not move from the interior of the conduit into defects in the wall of the conduit. Likewise, it does not provide for traversing a defect such as a severely offset joint or shear. Since the plug can only be pulled, it cannot advance once it has become wedged in place in such a defect.
The present invention provides a method for effectively sealing leaks in underground pipes such as sewer system piping, and which overcomes the aforementioned shortcomings and disadvantages of the previously known methods for repairing such sewer system piping. The method of the invention in a most basic preferred embodiment includes the steps of isolating a section of a system of drainage piping from active use; thereafter blocking existing defects against further intrusion of ground water by pressurizing and everting a flexible liner and containment tube within the section of piping to be repaired, utilizing pressure greater than the pressure of ground water attempting to intrude through defects in the piping; continuing to maintain pressure within the interior of the piping to be repaired while installing a fluid sealant material within the piping and forcing effective quantities of the sealant material into and outwardly through defects existing in the pipe walls by filling a portion of the pipe with such fluid sealant material under adequate pressure; thereafter, while still maintaining pressure greater than the pressure of ground water attempting to intrude through defects in the pipe, again everting the liner and containment tube into the portion of the pipe to be repaired and keeping the liner and containment tube in place, holding the sealant material in position while it cures in place to plug openings through the wall of the piping and to form a barrier on an exterior surface of the piping where sealant material has been forced outwardly through effective portions of the piping.
In accordance with one aspect of the present invention a fluid (such as water or air) used to fill the liner and containment tube may be used to carry heat to or away from the material of the piping being repaired in order to provide an environment having a required temperature to facilitate use of a particular sealant material to plug and seal defective portions of the piping.
According to one aspect of the present invention the flexible liner and containment tube can be used to sustain pressure on the fluid sealant in order to force it into leaking openings in a wall of a pipe to be repaired and thereafter to hold the sealant material in place while it cures.
In accordance with a method that is one embodiment of the present invention a quantity of fluid sealant is moved to different locations, along a length of a section of piping being repaired, by the use of coordinated extension and retraction of a plurality of everted liner and containment tubes within an underground piping system being repaired.
In accordance with a novel method that is a further embodiment of the present invention pressure is maintained within everted liner and containment tubes within interconnected portions of an underground piping system so as to maintain sufficient pressure on a quantity of fluid sealant within one or more portions of such a piping system and thus to force effective quantities of such fluid sealant into voids adjacent to defects that provide openings through the walls of underground pipes being repaired.
In accordance with another aspect of the present invention, everted liner and containment tubes are used to move excess quantities of fluid sealant material to locations, within a portion of a piping system being repaired, where such excess sealant material can be removed from the pipe while such everted liner and containment tubes are maintained under sufficient pressure to hold fluid sealant material in a required location to seal defects in the portion of a piping system being repaired as the sealant material cures.
In accordance with one embodiment of the present invention a fluid sealant material has a density at least about equal to the specific gravity of water so that water in the piping being repaired does not displace the sealant material.
In accordance with another embodiment of the present invention, a mixture of fluid sealant material incorporates a hydrophillic material in a quantity sufficient to cause the sealant material to swell within an opening, such as a crack or similar defect in a wall of a pipe being repaired or in the porous strata surrounding the pipe, and create a tight seal within such a defect or form a barrier outside the pipe.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.